The present invention relates to decorative lighting and in particular to a thermally efficient liquid motion lamp.
Liquid motion lamps, commonly called “lava lamps”, have been known since the 1960s. Such lamp is described in U.S. Pat. No. 3,387,396 for “Display Devices.” The '396 patent describes a lamp having globules of a first liquid suspended in a second liquid, wherein the first liquid has a thermal expansion coefficient providing sufficient expansion, and therefore reduction in density, such that the first liquid is heavier than the second liquid at a lower temperature, and lighter than the second liquid at a higher temperature. The temperatures may be, for example, 45 degrees Centigrade and 50 degrees Centigrade. The first and second liquids are contained in a clear container having a heat source at the bottom, and as a result, the first liquid is heated, rises within the second liquid, cools, and drops back to the bottom of the container. At least one of the liquids is preferably colored, and provides an entertaining motion for an observer. Lamps such as described by the '396 patent are typically small and are sold as a sealed unit.
Unfortunately, known lamps often exhibit erratic behavior because of temperature fluctuations. The internal lamp temperature fluctuates with ambient temperature and the liquids fail to behave as intended. Further, high temperatures can cause the liquids to break down.
Recently, liquid motion lamps have gained popularity, and there is a desire to use such lamps in various commercial settings, for example hotel lobbies, clubs, lounges, etc. There is a desire that such lamps used in a commercial setting be substantially larger than known liquid motion lamps, but shipping such large lamps filled with liquid results in a high probability of damage and high shipping costs. U.S. Pat. No. 7,137,720 filed Jun. 1, 2004 by the present applicant discloses a liquid motion lamp which may be shipped dry, and filled with a liquid at it's final destination. The dry shipment thus makes large liquid motion lamps much more practical. However, such large lamps are being used in luxurious settings where the appearance of the motion in the lamps is very important, and the large lamps may not behave consistently due to temperature fluctuations, particularly with tall lamps, for example, over five feet high. If the temperature is not carefully controlled, the desired visual affects may not be achieved. For example, too high of temperatures may cause the first liquid to remain near the top of the container, and cause clouding. Too low of temperatures will result in the first liquid failing to rise a desired amount.
U.S. Pat. No. 7,478,914 for “Control System for Liquid Motion Lamp” describes a lamp with temperature sensors and two heating elements to control the temperature of liquids contained in the lamp. One heating element is an incandescent light in the base of the lamp producing both light and heat and the other heating element may be a submerged heating element, a heat blanket wrapped around the base of the liquid container, or other heating element. A sensor is provided to measure the temperature of the liquids inside the lamp and the control system controls both heaters to maintain the temperature within preferred operating limits. While the sensor, heating elements, and control system of the '914 patent address problems of known liquid motion lamps, the radiation from the incandescent light is mostly outside the visible spectrum and results in significant heating of the base of the lamp. Additionally, the incandescent light often generates more total energy than is needed to maintain the temperature of the liquids for proper operation, and over temperatures have resulted, reducing the life of chemicals in the liquids. Further, such liquid motion lamps are often used in crowded bars and lounges which are often at elevated temperatures, and the added heat generated by the incandescent light adds to the hot environment adding to the discomfort created by the heat and/or to air conditioning costs. Incandescent lights for a small commercial lamp (about 11 gallons of liquids) may require 250 watts of power and incandescent lights for a larger commercial lamp (about 22 gallons of liquids) may require 350 to 400 watts of power. Small consumer lamps (one to 3 gallons of liquids) generally use 100 watt incandescent lights which result in overheating the liquids in a hot room. Further, experiments have show remarkable effects when brighter lighting is used, but such brighter lighting produces too much heat using known incandescent lights. The incandescent lights may also have a short operating life and require frequent replacement. The '720 and '914 patents are herein incorporated in their entirety by reference.